Flow Triggered Gas Delivery

ABSTRACT

A fluid delivery system provides fluid, such as supplement oxygen, to a patient in response to inhalation. The fluid delivery system includes a valve assembly that is triggered by sensing onset of inspiration by measuring a change in temperature or fluid flow of air flow in a nasal or oral cannula, mask or helmet.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part (CIP) of our copending U.S.patent application Ser. No. 17/199,172, filed Mar. 11, 2021 which inturn is a continuation-in-part (CIP) of our copending U.S. patentapplication Ser. No. 16/986,017, filed Aug. 5, 2020, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

The present disclosure relates to devices and methods for monitoring anddelivering oxygen or other gas to a human or other animal, and foreffectively conserving the delivery of said gas. The disclosure hasparticular utility for delivery of supplemental oxygen to a human oranimal patient and will be described in connection with such utility,although other utilities are contemplated.

In the U.S. today well over 1.5 million human patients are receivingsupplemental oxygen therapy at a cost believed to be excess of 2 billiondollars annually. Moreover, acute cases due to COVID-19 have exacerbatedthe demand for supplemental oxygen to a point where some hospitals arerunning out of oxygen supplies.

Most of the patients receiving long term supplemental oxygen therapy(LTOT) suffer from chronic hypoxemia as a result of having a chronicobstructive pulmonary disease (COPD). Presently there is no cure forthis condition. However the detrimental impact of chronic hypoxemia maybe mitigated by the administration of long term oxygen therapy (LTOT).The continuous inhalation of low flows of oxygen, typically 2-3 lpm(liter per minute), from a nasal cannula increases the concentration ofoxygen that the patient is breathing. It is estimated that for each 1lpm flow, the overall inhaled concentration rises by 3-4%. The increasein oxygen concentration compensates for the poor function of thepatient's lungs in absorbing oxygen.

Generally when a patient is diagnosed with chronic hypoxemia, oxygen isprescribed at a fixed flow rate based on a 20-minute titration test inthe doctor's office. During the test, the patient's blood oxygensaturation is measured by either using an invasive blood gas analyzer ora non-invasive device such as a pulse oximeter. While measuring theblood saturation (SpO₂), the patient may be asked to walk on a treadmillso as to measure his or her need for supplemental oxygen while exertinghim or herself. Based on this brief test, a fixed flow of supplementaloxygen is prescribed. The patient may be advised to increase the flowrate of supplemental oxygen during exertion, for example, while climbingstairs, while sleeping or if they feel short of breath. The patient willneed confirmation of the adequacy of supplemental oxygen treatment, withthe goal of keeping the patient's oxygen saturation above 90% during allof their activities, including during sleep. Some patients may beprescribed supplemental oxygen to breathe 24 hours per day or may onlyrequire supplemental oxygen while ambulating or may need supplementaloxygen treatment only when sleeping. Among patients requiring LTOTduring their waking hours, often higher flow rates are required whilesleeping. It is common practice to increase the flow rate by 1 liter permin while a patient is sleeping.

If a patient needs to breathe supplemental oxygen even while resting, heor she will be given a stationary oxygen generating unit in his or herhome which can be set to produce, e.g., up to 5 liters per minute of 93%oxygen. Generally, the units today are manually set to a prescribed flowrate in liters per minute. If a patient requires supplemental oxygenwhile ambulating, he or she typically will carry small high pressureoxygen cylinders or small refillable liquid oxygen dewars. Smallportable oxygen generators are also available which can produce up to 3liters per minute of continuous oxygen or deliver pulsed oxygen athigher flow rates. These portable oxygen delivery systems all havedrawbacks. Portable concentrators are usually bulkier and noisier andhave a relatively short battery life. The small high pressure oxygencylinders have restricted capacity, especially the smaller ones, but donot need a battery or make the kind of noise produced by theconcentrators.

Due to the expense of providing oxygen in small cylinders and dewars forambulation, various oxygen conserving devices have been developed toconserve the oxygen flow. These prior art oxygen conserving devices onlydeliver short pulses of oxygen at the beginning of a patient'sinhalation. By not delivering oxygen during exhalation or the laterperiod of inhalation, the oxygen which would have had no impact onincreasing the patient's oxygen saturation is conserved. There nowexists both pneumatic and electronic oxygen conserving devices whichclaim to achieve oxygen conserving ratios from 2:1 to 7:1 compared tothe delivery of continuous oxygen flow. Such higher conservation ratiosare achieved by the electronic devices which are programmed to skipbreaths so that oxygen pulse is only delivered every other breath.However, electronic devices cannot be used on all ambulating patientssince such high conservation ratios can actually result in poor oxygensaturation for the patient particularly during periods of increasedoxygen utilization as in walking vigorously or walking up stairs.

Moreover, currently available conserving devices measure a drop in nasalair pressure, which for many patients is inadequate to trigger therelease of oxygen under various circumstances, including: extremelyreduced respiratory function; most mouth breathing; talking whilewalking; while walking briskly or while talking intensely; or whilesleeping. Upon initiation of these ambulatory devices, patients are“taught” to focus on nasal breathing to help trigger the device. Often apatient needs to stop his or her activity and focus on his or her nasalbreathing, or to put the nasal cannula probe in his or her mouth to moreeffectively trigger the device.

Pressure sensing of the onset of inhalation in electronic oxygenconservers is currently is accomplished in one of two ways:

1. Some prior art designs employ a dual lumen cannula in which one ofthe lumens is dedicated to pressure sensing while the other is dedicatedto the supply of oxygen. This design is meant to be more sensitive tothe onset of inhalation but suffers from the drawback of only being ableto deliver oxygen to one of the nasal passages.

2. Other designs use a single lumen cannula that typically has apressure sensor connected to a T piece below two nasal prongs. Overallpressure drop associated from inhalation is sensed from both nasalpassages and oxygen is then delivered to both nasal passages.

Both designs suffer from a delay in triggering a flow of oxygen due tothe hysteresis which is inherent in pressure sensing. However, even aslight delay in triggering a flow of oxygen is readily perceived by thepatient. Another drawback of current designs using pressure sensors isthat if one of the patient's nasal passages is blocked, it willinterfere with the detection and delivery of oxygen.

Yet another flaw with current oxygen generating systems is the fact thata patient's ideal need for oxygen varies with time both in the shortterm as a result of varying exertion and in the long term as a result ofimprovement or deterioration in health. When a doctor prescribes a fixedflow rate of oxygen for a patient, the doctor is mainly concerned withensuring that the patient's blood saturation does not drop below anoxygen saturation of 88-89%. The doctor does not want to have a patientexperience desaturation of oxygen below 90% during any of the patient'sactivities. Although there exist theoretical concerns about potentialtoxicities in patients administered oxygen in high concentrations (above50 percent) for extended time periods (e.g., absorptive atelectasis,increased oxidative stress, and inflammation), clinical experience hasprovided little support for these concerns in the setting of LTOT.(“Long-term supplemental oxygen therapy.” Up-To-Date; Jan. 18, 2013.Brian L Tiep, MD Rick Carter, PhD, MBA).

Current oxygen treatment plans are prone to error as reported by a studyby Fussell et al. (Respiratory Care. February 2003, Vol. 48 No. 2). Inthat study, blood saturation levels of 20 patients suffering from COPDwere monitored continuously using pulse oximetry to confirm if eachpatient's oxygen prescription adequately maintained his or hersaturation. The conclusion of the study was that there was a poorrelationship between conventional oxygenation assessment methods andcontinuous ambulatory oximetry during LTOT screening with COPD patients.More recently in an article entitled “Critical Comparisons of theClinical Performance of Oxygen-conserving Devices,” Am. J. Respir. Crit.Care Med. 2010 May 15; 181(10): 1061-1071, the current collection ofconserving devices all based on pressure sensing were criticized asfailing to deliver on their efficacy claims. The authors claimed that“Although each device activated during nose and mouth breathing, noneconsistently performed according to engineering expectations.”

When a patient obtains low oxygen saturation results while usingconserving devices or fixed oxygen flow rates, the natural response isto simply increase the flow rate, when in actuality, low oxygensaturation results often are caused by a delay in triggeringsupplemental oxygen flow as early as possible at onset of inhalation.Increased nasal flow rates become increasingly expensive and aregenerally not well tolerated. Some COPD patients who use stationaryoxygen concentrators in their homes are financially impaired and areconcerned about the power costs of continuously running an oxygenconcentrator. In many cases this has led to a compliance issue where thepatient may elect to not switch on the concentrator and follow thetherapy as prescribed by the doctor in order to save on theirelectricity bill. Moreover, these oxygen concentrators throw a fairamount of heat into the room, which may further add to energy costs,i.e., for cooling the room. Current oxygen concentrator designstypically will produce a maximum flow rate, e.g., of 5 liters perminute. If a patient's resting prescription is 2 liters per minute, thepatient may set a flow rate through their cannula to the required flowand the excess oxygen that is being produced is simply pushed into thenostrils which while mouth breathing may be wasted. Many oxygen therapypatients can spend a significant amount of their time while active, ortalking, or napping, or sleeping with blood oxygen saturation levelsthat are unacceptable.

Current pressure-based oxygen conserving units fail to live up to theirclaims when a patient is mouth breathing during more vigorous activity,while talking, while eating and/or when sleeping. Often patients onambulatory oxygen will have to stop and focus on their nose breathing,or put the nasal cannula prongs in their mouth and suck on them totrigger the release of oxygen. When oxygen needs are not being met, thesimple solution is to increase the nasal flow rate, which causesincreasing problems of uncomfortable nasal passage drying and sometimesnasal mucosal bleeding. Further, patients often stop their oxygendelivery system altogether when eating.

In my prior U.S. Pat. No. 9,707,366, I describe an improved system,method and apparatus for controlled delivery of oxygen to patient inwhich a nasal cannula or a combined nasal and oral cannula with a valveassembly and a flow sensor for sensing “flow leakage” through apatient's nasal cavity, while they are breathing. This “hidden signal,”coupled with simultaneous monitoring of nasal and/or oral flow patterns,enables an on-demand oxygen delivery system without uncertainty ormisdirected oxygen—both of which lead to oxygen wastage, or inadequateoxygen delivery to the patient. More particularly, my prior '366 patentdescribes a fluid delivery system comprising at least one source offluid; at least one valve assembly coupled to said at least one sourceof fluid, wherein the at least one valve assembly is configured to allowflow of fluid from the at least one source during patient inspiration;an outlet end comprising a nasal or oral cannula in fluid communicationwith the at least one valve assembly; and a nasal flow sensor fortriggering fluid delivery in response to patient inspiration. The fluiddelivery system further including a power source configured to operatethe at least one valve assembly. The location of the nasal flow sensormay be in or adjacent the nasal cannula or oral cannula, adjacent thefluid source, or in air tubing between the nasal cannula or oral cannulaand the at least one source of fluid.

SUMMARY OF THE DISCLOSURE

The present disclosure provides improvements over the method andapparatus of my prior '366 patent by providing an improved triggermechanism for triggering the valve to release fluid from the fluidsource for delivery to the patient via the nasal or oral cannula. Thefluid delivered by the method may comprise oxygen. More particularly,the present disclosure in one aspect provides a flow sensor that employsheater(s) and temperature sensor(s) to detect onset of inspiration bymeasuring a temperature differential caused by the convective coolinginduced by the flow of the fluid, and trigger flow within less thanabout 20 milliseconds, typically within 10-20 milliseconds of the onsetof inspiration, which is far better than any currently availablepressure sensor is capable of providing.

Also, to permit the use of a high sensitivity air flow sensor, toprotect the sensor from high pressure oxygen flow, the presentdisclosure preferably isolates the air flow sensor from the oxygen flowline via a switching valve.

In one aspect of the disclosure there is provided a fluid deliverysystem for controlling delivery of a fluid to a human or animalcomprising at least one source of said fluid; at least one valveassembly coupled to said at least one source of said fluid, wherein theat least one valve assembly is configured to allow flow of said fluidfrom the at least one source during said human or animal inspiration; anoutlet end comprising a nasal or oral cannula in fluid communicationwith the at least one valve assembly; and a flow sensor for triggeringfluid delivery in response to said human or animal inspiration, whereinthe flow sensor is in fluid communication with and upstream the nasal ororal cannula, and includes a temperature sensor such as a thermistorconfigured to detect a change in temperature indicative of onset ofinspiration by said human or animal, within less than about 20milliseconds, typically within 10-20 milliseconds of said onset ofinspiration. The system also may include a power source configured tooperate the at least one valve assembly.

In another aspect of the disclosure the flow sensor is located in oradjacent the nasal cannula or oral cannula, or is located in tubingconnective the nasal cannula or oral cannula and the at least one sourceof said fluid. Preferably, the fluid delivered preferably comprisessupplemental oxygen, a therapeutic gas or an anesthetic gas.

The present disclosure also provides an apparatus for conserving fluidbeing delivered from a fluid supply to a human or animal comprising: afluid conserver controller connected between the fluid supply and anasal cannula or an oral cannula, wherein said controller comprises atleast one valve triggered selectively to deliver said fluid to the nasalor oral cannuli; a flow sensor configured to sense inspiration by humanor animal; and a trigger mechanism, communicating with said sensor foractuating the conserver controller, wherein the flow sensor is in fluidcommunication with said nasal or oral cannula, and includes atemperature sensor such as a thermistor configured to detect a change intemperature indicative of onset of said inspiration by said human oranimal, within less than about 20 milliseconds, typically within 10-20milliseconds of said onset of inspiration.

In one embodiment of the disclosure the flow sensor and triggermechanism are remote from one another, and the flow sensor and thetrigger mechanism communicate either by wire or wirelessly.

In a preferred embodiment of the disclosure, the flow sensor and triggermechanism are remote from one another, and the flow sensor and thetrigger mechanism communicate either by wire or wirelessly.

In a preferred embodiment of the disclosure the at least one valvecomprises at least one valve, and the fluid supply preferably comprisesoxygen, a therapeutic gas or an anesthetic gas.

In another preferred embodiment of the disclosure, the flow sensorcomprises a MEMS flow sensor, preferably a MEMS piezoresistive flowsensor, or a MEMS thermal flow sensor, preferably a MEMS thermal massflow sensor, or a MEMS ultrasonic transit time flow sensor.

The present disclosure also provides a method for conserving delivery ofa fluid from said fluid source to a patient, comprising the steps of:providing a valve in communication with a fluid source and a nasal ororal nasal cannula worn by the patient; sensing, with a flow sensorincluding a temperature sensor such as a thermistor in communicationwith the nasal or oral cannula, onset of inspiration by detecting achange in temperature of airflow through said nasal or oral cannula,within not more than about 15-20 milliseconds of said onset ofinspiration, triggering the valve, in response to the sensed onset ofinspiration to release said fluid from the fluid source for delivery tothe patient via the nasal or oral nasal cannula preferably the fluidcomprises oxygen, a therapeutic gas of an anesthetic gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood from a reading of the followingdetailed description taken in conjunction with the drawings in whichlike reference designators are used to designate like elements, and inwhich:

FIGS. 1 and 2 are block diagrams of two different systems for fluiddelivery in accordance with the present disclosure;

FIG. 3 is a block diagram of a remote sensor and control in accordancewith a preferred embodiment of the present disclosure;

FIG. 4 schematically illustrates the triggering algorithm in accordancewith a preferred embodiment of the present disclosure;

FIG. 5 is a table comparing the onset of gas flow delivery by the systemof the present disclosure with conventional prior art systems employingpressure flow sensors;

FIG. 6 schematically illustrates a MEMS thermal mass flow sensor usefulin accordance with the present disclosure; and

FIG. 7 schematically illustrates an ultrasonic flow meter useful inaccordance with the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

As used herein “nasal cannula” is intended to include two lumen nasalcannuli as well as nasal masks or pillow masks. And “oral cannula” isintended to include face masks as well as breathing tubes, mouth piecesand the like, as well as diver and hazard helmets and the like.

Embodiments are described in the following description with reference tothe drawing figures in which like numbers represent the same or similarelements. Reference throughout this specification to “one embodiment,”“an embodiment,” “certain embodiments,” or similar language means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment of thepresent disclosure. Thus, appearances of the phrases “in oneembodiment,” “in an embodiment,” and similar language throughout thisspecification may, but do not necessarily, all refer to the sameembodiment.

The described features, structures, or characteristics of the disclosuremay be combined in any suitable manner in one or more embodiments. Inthe following description, numerous specific details are recited toprovide a thorough understanding of embodiments of the disclosure. Oneskilled in the relevant art will recognize, however, that the disclosuremay be practiced without one or more of the specific details, or withother methods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the disclosure.

The fluid delivery system of the present disclosure providessupplemental oxygen, to a human or animal in intermittent timeintervals, based on the patient's tidal breathing. The fluid deliverysystem includes a nasal or oral nasal flow-triggered valve assembly thatopens in response to a patient's inhalation, and closes during theinspiratory phase to conserve oxygen which would otherwise be wasted onfilling up a patient's “dead space” prior to the end of inhalation. Thatis to say, the present disclosure senses onset of inspiration, through atemperature sensor placed in a nasal cannula or oral cannula, or supplytube in the case of a helmet, and triggers the regulator valve to openupon onset of inhalation, i.e., within not more than about 15-20milliseconds of onset of inhalation, and to remain open for a period oftime consistent with the human or animal's tidal breathing.

The nasal or oral flow temperature sensor is sensitive enough to senseonset of inspiration within less than about within 20 milliseconds,typically within 10-20 milliseconds, and send a signal to the valveassembly to open and permit flow of oxygen for a period of time. Byopening within not more than about 20 milliseconds, typically within10-20 milliseconds after onset of inspiration, and then staying open fora limited period of time, it is possible to achieve a truly on-demandoxygen delivery system without uncertainty or misdirected oxygen—both ofwhich lead to oxygen wastage or inadequate oxygen delivery to thepatient. With onset of inspiration flow information, the waste involved,for example, with pulse regulated oxygen or continuous flow oxygen iseliminated. Moreover, the patient or user has a pleasing sense ofsynchrony between breath initiation and delivery of oxygen and, byeliminating any perceptible delay in oxygen delivery, feels free to moveabout and talk spontaneously without fear of missing his or her oxygenpulse. Also the efficiency of conserving devices can be utilized inhospitalized or bedridden patients from a central liquid supply with areliable pulse oxygen delivery system.

Moreover, unlike pressure flow sensors described in the prior art,sensing and thus triggering using a temperature sensor in accordancewith my disclosure is essentially instantaneous, i.e., within less thanabout 20 milliseconds, typically within 10-20 milliseconds of onset ofinhalation. Thus, there is essentially no delay delivering supplementaloxygen. Nor is there any waste of oxygen compared to conventionalpressure flow-sensor detectors. Consequently, the flow of supplementaloxygen is turned on essentially with onset of inhalation, and timed toremain on for a period of time in concert with the ramp up of thepatient's tidal breathing and/or upon detection of the onset ofexhalation. As a result, supplemental oxygen is conserved because thesupplemental oxygen is not provided when the patient does not need theoxygen: during the filling of “dead space” (i.e., the volume of airwhich is inhaled that does not take part in the gas exchange), or duringexhalation.

As used herein, inhalation is used synonymously with inspiration, andexhalation is used synonymously with expiration. Inhalation is themovement of air from the external environment, through the airways, andinto the lungs. During inhalation, the chest expands and the diaphragmcontracts downwardly or caudally, resulting in expansion of theintrapleural space and a negative pressure within the chest cavity. Thisnegative pressure results in airflow primarily from either the nose orthe mouth into the pharynx (throat) and trachea, eventually entering thelungs. By using a flow sensor in the form of a temperature sensor, thedetermination of onset of inspiration is essentially instantaneous,i.e., within less than about 20 milliseconds, typically within 10-20milliseconds of onset of inspiration taking advantage of the mostimportant phase of inspiration to deliver supplemental oxygen. Althoughany bloused or pulsed oxygen delivery system is set as a flow rateequivalent, there is more consistency and parity with bolus amounts andcontinuous flow rates. The term “pulse equivalent” which is presumedcomparable to continuous flow is how current conserving regulators areset. Continuous flow rates are set at liters per minute.

Since pulse units do not put out continuous oxygen, they cannot bemeasured in liters per minute. Instead, they are classified by size ofthe individual pulse (bolus), i.e., how often that pulse can bedelivered in a minute, and when the pulse is delivered in theinspiratory (breathing) cycle. The other issue for pulsed oxygenconcentrators which can be limiting is when a patient tries to take morebreaths per minute than the unit is capable of producing. When thisoccurs, the oxygen user will either get a smaller pulse, a pulse withless oxygen, or no pulse at all. In a situation where the oxygen userexerts and become significantly out of breath, the unit may fail to meetthe user's needs. With a nasal or oral flow temperature sensor inaccordance with the present disclosure, we are able to get closer to theequivalent of continuous oxygen flow since the oxygen is deliveredessentially immediately (i.e., generally within less than about 20milliseconds, typically within 10-20 milliseconds of the onset ofinhalation after the user begins to inhale air). Without the delayinherent in the pressure sensor method of triggering oxygen release aspreviously discussed, there is no need to push up the bolus amount tomake up for the delay in delivery.

Also using onset of inhalation flow triggered pulse oxygen in accordancewith the present disclosure, due to the increase in sensitivity indetecting onset of inspiration, the user does not have to think how heor she is breathing—the trigger senses onset of inspiration by atemperature drop through the flow sensor even when the patient is mouthbreathing or while talking, walking and talking, or eating. It does notmatter if the user has large nostrils or if the user is dozing in achair, or sleeping. There is no required training—the user just placesthe cannula in his or her nostrils or mouth and experiences essentiallysynchronous oxygen delivery. As noted supra, conventional pressureflow-triggered pulse oxygen delivery has a noticeable delay in the“puff” of oxygen delivered, while onset of inspiration-flow-triggeredoxygen delivery using temperature drop in accordance with the presentdisclosure has essentially no perceivable delay, giving it a morenatural feel. It releases the oxygen essentially as the user is inhalingnot after the user starts inhaling. Compared also to when using aconventional chest strain gauge to judge onset of inhalation, the flowsensor of the present disclosure triggered opening of the valve beforeany chest motion is detected! This improved synchronicity between onsetof inhalation and oxygen delivery is more comfortable, more efficaciousand more reliable, and since it actually performs what other types ofconserving units only claim to do, will yield better patient compliance.

Additional uses of the present disclosure are in the diagnostic field ofsleep disorders. Much attention has been directed toward sleep studiesto confirm the diagnosis of sleep apnea, which is being diagnosed bothin sleep labs and home sleep studies. The sensing and documentation ofbreathing during sleep can be enhanced by measuring inspiratory flowmore accurately. Thus the same nasal flow temperature sensor which cantrigger pulse oxygen delivery also can be adapted to efficiently measurebreathing during diagnostic evaluations. Patients who have sleep apneaor periodic breathing and are only using oxygen supplementation also canuse pulsed oxygen delivery safely. This device can now allow patientswho use C-PAP or Bi-PAP machines to take advantage of the efficiencybenefits of pulsed oxygen delivery—delivering supplemental oxygen onlyduring inspiration. This is an improvement over the current method ofjust adding oxygen to the hose traveling to the mask, which provides amost inefficient oxygen delivery system given the built-in mask ventingas well as the inadvertent mask leaks which occur during the night.

Onset of inspiration-triggered oxygen delivery in accordance with thepresent disclosure also can free up traveling patients who are currentlylimited to 3 liters per min continuous flow rates. With portableconcentrators, setting a pulse rate of 4-6+ liters per min whilesleeping is just not reliable (“Critical Comparisons of the ClinicalPerformance of Oxygen-conserving Devices,” Am. J. Respir. Crit. CareMed. 2010 May 15; 181(10): 1061-1071; Published online 2010 Feb. 4. doi:10.1164/rccm.200910-1638OC PMCID: PMC2874449). These pulsed high flowdevices claim to be able to oxygenate patients while sleeping, but mosthealthcare providers do not consider pulsed high flow devices toreliably deliver sufficient oxygen to sleeping patients.

Onset of inspiration triggered oxygen delivery in accordance with thepresent disclosure also can be adapted to “piggyback” onto hospital andclinic central liquid oxygen systems at the point of delivery, providingefficiency where none exists currently.

Referencing now to FIGS. 1-3 of the drawings, FIG. 1 is a block diagramillustrating the components of the enclosure of the fluid deliverysystem 100 in accordance with a first exemplary embodiment of thepresent disclosure. More particularly, FIG. 1 illustrates the fluiddelivery system with a manual bypass valve configuration.

The system 100 includes an enclosure 120 which may be a housing orsimilar structure which contains the various components used for fluiddelivery, such that a supply of oxygen (O2) 110 can be delivered to apatient 114. The oxygen supply 110 may include an oxygen tank 110A, apiped oxygen supply 110B from a hospital or other medical facility, oranother device for suppling oxygen. Within the enclosure 120, the system100 includes a pressure regulator 122 which is connectable to the oxygensupply 110 and regulates the pressure at which oxygen is introduced tothe system 100. The oxygen supply 110 may be removably attachable to thesystem 100 using a connector of the pressure regulator 122. The pressureof the oxygen supply may be substantially high, such as up to 3,000 PSIin some situations, and on the outlet side of the pressure regulator122, the pressure may be lowered to the desired PSI, such as 15 PSI inone example. Receiving the oxygen from the pressure regulator 122 is amanual bypass valve 124, which allows for manual control of oxygendelivery to the patient 114. Specifically, the manual bypass valve 124may allow the user to select oxygen delivery along a first path, wherepulsed oxygen delivery is controlled by the electronic controller 126,known as ‘pulsed mode’, or along a second path which substantiallybypasses the controller 126 and delivers the oxygen directly ornear-directly to the patient 114, known as ‘bypass mode’.

When in pulsed mode, i.e., when the manual bypass valve 124 ispositioned to deliver oxygen to the patient which is controlled by thecontroller 126, the oxygen is directed to a valve 128, which may be a3-port piezo electric valve or another type. When the valve 128 is in anunenergized state, it blocks the flow of oxygen therethrough, and whenenergized or activated, it opens one or more of the valve ports to allowthe flow of oxygen through it. The supply of oxygen to the valve 128 isalso in fluid communication with an oxygen pressure sensor 130 which isconnected to the controller 126, such that the pressure of the oxygencan be sensed. Alternatively, the pressure sensor may comprise a digitalpressure sensor with an SPI interface. The output of valve 128 isconnected to the oxygen output 132 of the system 100 which leads to thepatient 114. As shown in FIG. 1, oxygen delivery to the patient mayinclude various tubing with a nasal cannula 143 which can be positionedproximate to the patient's nose, however other delivery systems also maybe used, including face masks, mouth pieces or the like.

The controller 126 also includes electronic control components, such asmicrocontrollers, circuits, input and output devices, or othercomponents which control activation and use of the system 100, which aredescribed in detail relative to FIG. 3. In general terms, the controller126 is in communication with valve 128, the oxygen pressure sensor 130,an indicator device 134, an ambient air supply 136, and a power supply138. The ambient air supply 136 may include a port in the enclosure 120which intakes ambient air and passes it by an air flow sensor 140. Airflow sensor 140 is in communication with the nasal cannula 143 andprovides the processor or microcontroller with a reading of the ambientair flow and senses onset of inspiration as well as discussed below. Theoutput of the ambient air supply 136 may be delivered to the patient 114using tubing and a cannula, mask, mouth piece or other deliverycomponents, or via ambient air outlet 142 and dual lumen cannuli asillustrated in FIG. 2.

The indicator device 134 may include a variety of indicator types, suchas in one example, a keypad with visual indicators. Other types ofindicators may also be used. The visual indicators of the indicatordevice 134 may include visual indicators for operations includingstandby, pulse control, sensitivity, bypassed or pulsed delivery, forpower level, and for an alarm. Commonly, the indicator device 134 may besubstantially integrated into the enclosure 120, but it also may be afully or partially separate device. The power supply 138 may include oneor more different electrical power supply devices such as a hardwireddevice, e.g., a 115/230 VAC supply, user-replaceable batteries,user-replaceable batteries which are capable of being recharged, orinternal rechargeable batteries which may or may not be replaceable.Naturally, the power supply 138 may include combinations of these orother power sources to ensure continued operation of the system 100 inthe event that one of the power sources fails. The controller 126 mayinclude additional components, such as an audible alarm system 144 toprovide an audible alarm to the patient or another user, as needed.Additional components of the controller 126 are discussed relative toFIG. 2.

In operation, the cannula or other delivery device is positionedproximate to the patient's 114 mouth or nose. The system 100 receivesoxygen from the oxygen supply 110 and ambient air through the ambientair supply 136. When patient inhales, a negative pressure is applied tothe cannula tubing which is received at the oxygen output 132 and/or theambient air input 136. When in pulsed mode, the controller 126 isactivated and control pulsed oxygen is delivered to the patient.Activation of the controller 126 causes the controller 126 to energizethe piezoelectric valve 128, thereby opening a path for oxygen to flowfrom the oxygen supply 110, through the pressure regulator 122, throughbypass valve 124, and to the patient 114. The controller 126 may controlthe specific flow of oxygen to the patient 114, such as, for example, bycontrolling the onset of flow of oxygen pulse length, pulse rate, orother pulse characteristic at which oxygen is allowed to pass throughvalve 128, or by controlling the sensitivity of activation or one ormore components of the system 100. During control pulsed oxygendelivery, the patient 114 may continue to receive ambient air throughthe ambient air input 136.

The controller 126 may be activated manually such as with a button orswitch, or more preferably in accordance with the present disclosure,automatically through a sensed signal indicative of onset ofinspiration. In one example, the controller 126 may be activated bysensing a temperature change that results when the patient begins toinhale. In this example, a flow sensor in the form of a thermistor 140positioned in the path of the ambient air supply 136 is heated to atemperature above ambient, typically 10 to 20° C. above ambient. Whenthe user inhales, the in-line thermistor detects a drop in temperatureresulting from the flow of ambient air past the heated thermistor 140.When this drop in temperature is detected, an activation signal is sentto the valve 128 to release oxygen. Alternatively, it is possible toheat the air in the path of the ambient air supply 136 which is locatedproximate to the thermistor 140 to a temperature above ambient. When theuser inhales, a thermistor may be used to detect an increase intemperature of the ambient air flow supply as it passes by thethermistor 140, which in turn, can be used to send the activationsignal. In a preferred embodiment, thermistor is configured to measurechange in temperature in either direction, i.e., to measure a change intemperature on inhalation for triggering oxygen delivery, and to measurea change in temperature on exhalation, for triggering cessation ofdelivery of oxygen. Sensing the onset of exhalation also allows thesystem to deliver a single trigger for each inhalation. After sensinginhalation and triggering a pulse of fluid the system can preventtriggering again on the same inhalation by inhibiting any triggers untilexhalation is sensed.

In order to protect the flow sensor from the high pressure oxygen flowvalve 128 comprises dual actuator piezo valves 200, 202. Piezo valve 200is connected inline between the supplemental oxygen source 110 and theflow sensor board 140, while piezo valve 202 is connected on one side tosensor board 140 and open on the other side to ambient air. Isolatingthe flow sensor from the high pressure oxygen flow permits the use of ahighly sensitive flow sensor which in turn permits us to senseinhalation essentially immediately at onset, which in turn permits us totrigger a pulse of oxygen at the most opportune time, without waste.Prior art conservators which sense and deliver gas flow from the sameline and are unable to sense inhalation essentially immediately atonset. Also, by isolating the flow sensor, we eliminate anycontamination of flow from the users exhaust breath.

The description of the operation of the system 100 thus far is for whenthe system is in pulsed mode, i.e., where oxygen delivery is controlledby the electronic controller 126. Using the manual bypass valve 124,however, the user can change the system 100 from pulsed mode to bypassmode to deliver oxygen to the patient 114 directly. As shown in FIG. 1,in bypass mode, the supply of oxygen 110 from the pressure regulator 122may pass through the manual bypass valve 124 and be directed to theoxygen outlet 132 directly or nearly directly, since the oxygen may passthrough one or more dividing couplings. Thus, in bypass mode, the oxygenis delivered to the patient 114 without pulse control from thecontroller 126. Using the bypass valve 124, the user can control thedesired mode of operation of the system 100 as needed, depending on thepatient or the intended use of the system 100.

FIG. 3 is a block diagram illustrating an electrical block diagram ofthe controller 126 of the fluid delivery systems 100 and 102, of FIGS.1-2, respectively, in accordance with a third exemplary embodiment ofthe present disclosure. As shown in FIG. 3, the controller 126 includesvarious controller circuitry and processing modules which are incommunication with the components of the fluid delivery system. Allcomponents may be in communication with a microcontroller 150, which mayreceive signal and processing data from each of the components andcontrol processing functions.

The microcontroller 150 is connected to the oxygen sensor 130 or oxygentransducer resistor bridge, whereby the signal from the oxygen sensor130 is amplified with a bridge signal amplifier, and then input into themicrocontroller 150 through an ADC connection. An optional secondaryoscillator may be provided to the microcontroller 150. An internalfactory CAL switch or jumper may be connected to the microcontroller 150through a CAL switch circuit. The temperature of the ambient air supply136, which is sensed by the thermistor 140, may be connected to themicrocontroller 150 by a flow sensor circuit 152. Within the flow sensorcircuit 152, a heater control and one or more heater drivers may be usedto heat the thermistor 140 and/or the ambient supply surrounding it, andthe flow signal from the thermistor 140 is received back in the flowsensor circuit 152. The signal may be processed by offset adjust and/orspan adjust and then amplified before transmission to themicrocontroller 150. Alternatively, the flow sensor circuit may haveintegrated therein a heater driver and control circuit, digital potcircuits and a flow signal amplifier.

The piezoelectric valve 128 receives control signals from an oxygen portpiezo valve driver 154 and a flow sense port piezo valve driver 156,which are connected to the microcontroller 150. The oxygen port piezovalve driver 154 has a piezo driver DC-DC converter which is connectedto the power supply and an on/off signal, a voltage selector circuit,and FET switch controls. The flow sense port piezo valve driver 156 hasa second piezo driver DC-DC converter, a voltage selector circuit, andFET switch controls. During operation of either driver 154, 156, asignal from the voltage selector circuit is provided to a FB circuit,which provides a voltage feedback to the piezo driver DC-DC converter. Asignal from the microcontroller received at the FET switch controls istransmitted to the corresponding connect or drain switch for each driver154, 156. The resulting signals from the oxygen switch of oxygen portdriver 154 and the flow sensor switch of the flow sense driver 156 aretransmitted to the piezoelectric valve 128 to control energization andactuation.

The indicator device 134 may be connected to the microcontroller 150through one or more keypad button-press sense & LED driver circuits.Similarly, the audible alarm system 144 may be connected to themicrocontroller 150 using a buzz driver. The power supply 138, includinga hardwired power supply or battery power supply, may be connected tothe microcontroller 150 using a power source selection, which controlspower source distribution. Various voltage regulators and converters maybe used to facility powering the various circuits and components of thesystem for fluid delivery, either directly, or through themicrocontroller 150 as shown in FIG. 3. Additional power supplycomponents may also be included, such as a power input protectioncircuit, charging circuits, a battery voltage monitor, or others. Themicrocontroller 150 also may have an ADC test circuit 158 connectedthereto.

Further details of the present disclosure are found in FIG. 4 which is aschematic diagram illustrating the operation algorithm of a supplementaloxygen delivery system for the present disclosure and illustrates howafter sensing inhalation and triggering a pulse of fluid, the system canprevent triggering again on the same inhalation by inhibiting anyfurther triggers until exhalation is sensed.

FIG. 5 Table I which reports response times in triggering ofsupplemental oxygen flow following onset of inspiration of a patient inaccordance with the present disclosure using a temperature sensor,compared with triggering of supplemental oxygen flow following onset ofinspiration using the conventional pressure sensors, a Chad LotusTherapeutic Oxygen Conserver. Model OM-700, and a SmartDose OxygenConserver, Model CTOX-MN02. In tests, a temperature sensor flow sensorin accordance with the present disclosure was found to be 40 times moresensitive than conventional state of the art pressure flow sensor.

Although the present disclosure has been described in detail withreference to certain embodiments, one skilled in the art will appreciatethat the present disclosure can be practiced by other than the describedembodiments, which have been presented for purposes of illustration andnot of limitation. For example, referring to FIG. 6, various types ofthermal mass flowmeters may be employed for triggering the valveassembly to control the fluid of fluid. Thermal mass flowmetersgenerally use combinations of heated elements and temperature sensors tomeasure the difference between static and flowing heat transfer to afluid and infer its flow with a knowledge of the fluid's specific heatand density. The fluid temperature also may be measured and compensatedfor. If the density and specific heat characteristics of the fluid areconstant, for example, as in the case of bottled oxygen, the meter canprovide a direct mass flow readout, and does not need any additionalpressure temperature compensation over their specified range.

Referring to FIG. 7, an ultrasonic flow master also may beadvantageously employed. There are two main types of ultrasonicflowmeters: Doppler and transit time. While they both utilize ultrasoundto make measurements and can be non-invasive (measure flow from outsidea tube, pipe or vessel), they measure flow by very different methods.

Ultrasonic transit time flowmeters measure the difference of the transittime of ultrasonic pulses propagating in and against the direction offlow. This time difference is a measure for the average velocity of thefluid along the path of the ultrasonic beam. By using the absolutetransit times both the averaged fluid velocity and the speed of soundcan be calculated.

With wide-beam illumination transit time ultrasound can also be used tomeasure volume flow independent of the cross-sectional area of thevessel or tube.

Ultrasonic Doppler flowmeters measure the Doppler shift resulting fromreflection of an ultrasonic beam off the particulates in flowing fluid.The frequency of the transmitted beam is affected by the movement of theparticles; this frequency shift can be used to calculate the fluidvelocity. For the Doppler principle to work, there must be a high enoughdensity of sonically reflective materials such as solid particles or airbubbles suspended in the fluid. Due to this requirement, ultrasonicflowmeters cannot be used in my application.

Technological progress has allowed the manufacture of thermal massflowmeters on a microscopic scale as MEMS sensors; these flow devicescan be used to sense and measure flow rates in the range of nanolitersor microliters per minute. MEMS thermal flow sensors generally consistof two primary components: sensing and heater elements. The heattransfer difference between the working flow and heater is sensed by thesensing element, so the system's sensitivity increases as extra heatenergy is transmitted to the functioning fluid.

One of the key constraints affecting the precision of the standardtemperature-based flow sensors tends to be the proper preservation ofthe temperature of the sensing component. The failure to calculate lowflow velocities is another problem related to MEMS thermal flow sensors.The sensing components in conventional hot-film and hot-wire sensorshave a large specific heat capacity, which makes it difficult to trackthe low convectional heat transmission leading to low or bad frequencyresponse.

There are three kinds of MEMS thermal flow sensors H-type sensors orhot-film or hot-wire sensors that calculate flow by adjusting the powerof heat at a steady temperature or adjusting the temperature at steadypower of heat. The distinction among them is attributable to theirconstruction: the wire resistor in hot-film sensors is placed on amembrane next to the flux, whereas the resistor is independent of thesubstratum and located inside the flow in hot-wire type H sensors.C-type sensors, the second type, are calorimetric sensors that measurethe flow by measuring heat profile changes across the heater.Time-of-flight sensors are the third category that measures flow viaheat pulse recognition at a given distance from the heater.

Certain artificial and natural dielectric materials have the property ofpiezoelectricity, i.e., slow resistivity changes when influenced byexternal strain of stress, which allows them to generate electriccharges when a mechanical load is applied. This is also called thedirect piezoelectric effect. When used in MEMS flow sensors, theresistance change is mapped to a voltage signal that fluctuates as thevelocity of flow changes. On the other hand, if such materials areexposed to external electrical fields, dimensional or geometric changesare influenced. This effect is referred to as the converse piezoelectriceffect. A major piezoelectrical effect is illustrated in polymers suchas polyvinylidene fluoride (PVDF) and polycrystalline ferroelectricceramics including barium titanate (BaTiO3) or lead zirconate titanate(PZT). MEMS piezoelectric flow sensors are autonomous and thus don'tneed an external power source to achieve the sensor output signal.

The above described system also may be plugged into a conventional fixedflow regulator, or to a conventional hospital wall unit regulator, andconvert same to a “smart regulator”. The system also may be built intoor adapted as an add-on feature to a C-PAP mask. The system also may beused for controlling delivery of therapeutic gas such as nitric oxide oranesthetic gas, or for regulating flow of supplemental oxygen orbreathing gases for mountaineering and scuba applications, for fire andrescue protective gear, space suit applications and the like which mayemploy sealed helmets rather than nasal or oral cannuli, or masks. Thus,as used herein nasal cannula and oral cannula are intended to alsoinclude masks, sealed helmets, and the like. Still other changes arepossible. Therefore, the scope of the appended claims should not belimited to the description of the embodiments contained herein.

I claim:
 1. A fluid delivery system for controlling delivery of a fluidto a human or animal comprising: at least one source of said fluid; atleast one valve assembly coupled to said at least one source of saidfluid, wherein the at least one valve assembly is configured to allowflow of said fluid from the at least one source during said human oranimal inspiration; an outlet end comprising a nasal or oral cannula,mask or helmet in fluid communication with the at least one valveassembly; and a flow sensor for triggering fluid delivery in response tosaid human or animal inspiration, wherein the flow sensor is in fluidcommunication with and upstream the nasal or oral cannula, mask orhelmet and comprises a thermal sensor configured to detect a change intemperature indicative of onset of inspiration by said human or animal,within less than about 20 milliseconds, preferably 10-20 milliseconds,of said onset of inspiration.
 2. The fluid delivery system of claim 1,further comprising a power source configured to operate the at least onevalve assembly.
 3. The fluid delivery system of claim 1, wherein theflow sensor is located in or adjacent the nasal cannula or oral cannula,mask or helmet or is located in tubing connective the nasal cannula,mask or helmet or oral cannula and the at least one source of saidfluid.
 4. The fluid delivery system of claim 1, wherein the nasal andthe oral cannuli are coupled to each other.
 5. The fluid delivery systemof claim 1, wherein the fluid delivered comprises supplemental oxygen, atherapeutic gas or an anesthetic gas.
 6. The fluid delivery system ofclaim 1, further comprising electronic circuitry for controlling the atleast one valve assembly based on signals from the flow sensor.
 7. Thefluid delivery system of claim 6, wherein the electronic circuitrycomprises a trigger mechanism for actuating the release of said fluidthrough said at least one valve assembly.
 8. The fluid delivery systemof claim 6, further comprising a heater configured to heat the flowsensor or the fluid upstream of the flow sensor to above ambient,preferably 10-20° C. above ambient.
 9. The fluid delivery system ofclaim 1, wherein the thermal sensor comprises a MEMS thermal flowsensor, preferably a MEMS thermal mass flow sensor.
 10. The fluiddelivery system of claim 1, wherein the temperature sensor is configuredto detect the onset of inspiration and the onset of exhalation by adirectional change of temperature, and wherein the system optionallyincludes heaters located upstream and optionally downstream of saidtemperature sensor.
 11. The fluid delivery system of claim 1, whereinthe flow sensor is isolated from the at least one source of said fluidby a piezo actuator valve.
 12. An apparatus for conserving fluid beingdelivered from a fluid supply to a human or animal comprising: a fluidconserver controller connected between the fluid supply and a nasalcannula or an oral cannula, mask or helmet wherein said controllercomprises at least one valve triggered selectively to deliver said fluidto the nasal or oral cannuli, mask or helmet; a flow sensor configuredto sense inspiration by human or animal; and a trigger mechanism,communicating with said flow sensor for actuating the conservercontroller, wherein the flow sensor is in fluid communication with saidnasal or oral cannula, mask or helmet, and includes a temperature sensorconfigured to detect a change in temperature indicative of onset of saidinspiration by said human or animal, within less than about 20milliseconds, preferably 10-20 milliseconds, of said onset ofinspiration.
 13. The apparatus of claim 12, wherein said flow sensor andsaid trigger mechanism are remote from one another, and wherein saidflow sensor and said trigger mechanism communicate either by wire orwirelessly.
 14. The apparatus of claim 12, wherein the fluid supplycomprises oxygen, a therapeutic gas or an anesthetic gas.
 15. Theapparatus of claim 12, further comprising electric circuitry forcontrolling the at least one valve based on signals from the flowsensor.
 16. The apparatus of claim 12, further comprising a heaterconfigured to heat the flow sensor or the fluid upstream of the flowsensor to above ambient.
 17. The apparatus of claim 12, wherein the flowsensor is configured to detect the onset of inspiration and the onset ofexhalation by a directional change of temperature, and wherein thesystem optionally includes heaters located upstream and optionallydownstream of said temperature sensor.
 18. The apparatus of claim 12,wherein the flow sensor is isolated from the fluid supply by a piezoactuator valve.
 19. The apparatus of claim 12, wherein the flow sensorcomprises a MEMS thermal flow sensor, preferably a MEMS thermal massflow sensor.
 20. A method for conserving delivery of a fluid from afluid source to a patient, comprising the steps of: providing a valve incommunication with a said fluid source and a nasal or oral nasalcannula, mask or helmet worn by the patient; sensing, with a flow sensorin communication with the nasal or oral cannula, mask or helmet, onsetof inspiration by detecting a change in temperature of fluid throughsaid nasal or oral cannula, mask or helmet within less than about 20milliseconds, preferably 10-20 milliseconds of said onset ofinspiration, triggering the valve, in response to the sensed onset ofinspiration to release said fluid from the fluid source for delivery tothe patient via the nasal or oral nasal cannula, mask or helmet.
 21. Themethod of claim 20, wherein the fluid comprises oxygen, a therapeuticgas of an anesthetic gas.
 22. The method of claim 20, further comprisingheating the flow sensor or the fluid upstream of the flow sensor toabove ambient, preferably 10-20° C. above ambient.
 23. The method ofclaim 20, wherein the flow sensor comprises a temperature sensorconfigured to detect the onset of inspiration and onset of exhalation bydirectional change of temperature.
 24. The method of claim 20, includingthe step of isolating the flow sensor from the fluid source whilesensing onset of inspiration.
 25. The method of claim 20, wherein theflow sensor comprises a MEMS thermal flow sensor, preferably a MEMSthermal mass flow sensor.
 26. A fluid delivery system for controllingdelivery of a fluid to a human or animal comprising: at least one sourceof said fluid; at least one valve assembly coupled to said at least onesource of said fluid, wherein the at least one valve assembly isconfigured to allow flow of said fluid through a conduit from the atleast one source during said human or animal inspiration; an outlet endcomprising a nasal cannula, an oral cannula, a mask or a helmet in fluidcommunication with the at least one valve assembly; a MEMS flow sensorfor triggering fluid delivery in response to said human or animalinspiration, wherein the MEMS flow sensor is located at least in fluidcommunication with and upstream the nasal cannula, oral cannula, mask orhelmet and is configured to detect fluid flow indicative of onset ofinspiration by said human or animal, within less than 20 milliseconds,preferably 10-20 milliseconds, of said onset of inspiration.
 27. Thefluid delivery system of claim 26, further comprising a power sourceconfigured to operate the at least one valve assembly.
 28. The fluiddelivery system of claim 26, wherein the MEMS flow sensor is located intubing connecting the nasal cannula, the mask, the helmet or the oralcannula and the at least one source of said fluid.
 29. The fluiddelivery system of claim 26, wherein the fluid delivered comprisessupplemental oxygen, a therapeutic gas or an anesthetic gas.
 30. Thefluid delivery system of claim 26, further comprising electroniccircuitry for controlling the at least one valve assembly based onsignals from the MEMS flow sensor.
 31. The fluid delivery system ofclaim 30, wherein the electronic circuitry comprises a trigger mechanismfor actuating the release of said fluid through said at least one valveassembly.
 32. The fluid delivery system of claim 26, wherein the MEMSflow sensor is configured to detect a change of temperature of saidfluid in said conduit.
 33. The fluid delivery system of claim 26,wherein the MEMS flow sensor comprises a MEMS piezoresistive flowsensor, a MEMS thermal flow sensor, preferably a MEMS thermal mass flowsensor, or a MEMS ultrasonic transit time flow sensor.
 34. The fluiddelivery system of claim 26, wherein the sensor is configured to detectthe onset of inspiration and the onset of exhalation by a directionalchange of temperature, and wherein the system also includes two MEMSthermal flow sensors and a heater located between the two MEMS thermalflow sensors.
 35. An apparatus for conserving fluid being delivered froma fluid supply to a human or animal comprising: a fluid conservercontroller connected via a conduit between the fluid supply and a nasalcannula, an oral cannula, a mask or a helmet wherein said controllercomprises at least one valve triggered selectively to deliver said fluidto the nasal or oral cannula, mask or helmet; a MEMS flow sensorconfigured to sense inspiration by human or animal; and a triggermechanism, communicating with said MEMS flow sensor for actuating theconserver controller, wherein the MEMS flow sensor is located at leastin part in fluid communication with said nasal cannula, oral cannula,mask or helmet, and is configured to detect fluid flow indicative ofonset of said inspiration by said human or animal, within less than 20milliseconds, preferably 10-20 milliseconds, of said onset ofinspiration.
 36. The apparatus of claim 35, wherein said MEMS flowsensor and said trigger mechanism are remote from one another, andwherein said MEMS flow sensor and said trigger mechanism communicateeither by wire or wirelessly.
 37. The apparatus of claim 35, wherein thefluid supply comprises oxygen, a therapeutic gas or an anesthetic gas.38. The apparatus of claim 35, further comprising electric circuitry forcontrolling the at least one valve based on signals from the MEMS flowsensor.
 39. The apparatus of claim 35, wherein the MEMS flow sensor isconfigured to detect a charge of temperature of said fluid in saidconduit.
 40. The apparatus of claim 35, wherein the MEMS flow sensor isconfigured to detect the onset of inspiration and the onset ofexhalation by a directional change of temperature, and wherein thesystem also includes two MEMS thermal flow sensors and a heater locatedbetween the MEMS thermal flow sensors.
 41. The apparatus of claim 35,wherein the MEMS flow sensor comprises a MEMS piezoresistive flowsensor, a MEMS thermal flow sensor, preferably a MEMS thermal mass flowsensor, or a MEMS ultrasonic transit time flow sensor.
 42. A method forconserving delivery of a fluid from a fluid source to a patient,comprising the steps of: providing a valve in communication with a fluidsource via a conduit and a nasal cannula, an oral nasal cannula, a maskor a helmet worn by the patient; sensing, with a MEMS flow sensor incommunication with the nasal cannula, oral cannula, mask or helmet,onset of inspiration within less than about 20 milliseconds of saidonset of inspiration, wherein the MEMS flow sensor is located at leastin part in the conduit upstream of the sensor, and triggering the valve,in response to the sensed onset of inspiration to release said fluidfrom the fluid source for delivery to the patient via the nasal or oralnasal cannula, mask or helmet.
 43. The method of claim 42, wherein thefluid comprises oxygen, a therapeutic gas of an anesthetic gas.
 44. Themethod of claim 42, wherein the MEMS flow sensor is configured to detecta change of temperature of said fluid in said conduit.
 45. The method ofclaim 42, wherein the MEMS flow sensor comprises is configured to detectthe onset of inspiration and onset of exhalation by directional changeof temperature of fluid flow in said conduit.
 46. The fluid deliverysystem of claim 35, wherein the MEMS flow sensor is configured to detecta change of temperature indicative of onset of inspiration by said humanor animal within less than 10-20 milliseconds of said onset ofinspiration.